Optical: systems and elements – Lens – Including a nonspherical surface
Reexamination Certificate
2002-11-08
2004-11-02
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
Including a nonspherical surface
C359S722000, C359S738000, C369S044320, C369S112080
Reexamination Certificate
active
06813096
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical lens provided on an optical information recording and reproducing apparatus capable of conducting at least one of recording of information on an optical recording medium and reproducing of information recorded on an optical recording medium, and to an optical information recording and reproducing apparatus equipped with the optical lens mentioned above.
There has been known an optical pickup apparatus (optical information recording and reproducing apparatus) that conducts recording of information on an optical recording medium and reproducing of information recorded on an optical recording medium. In the optical pickup apparatus, a ray of light emitted from a semiconductor laser light source is converged on an information recording surface of an optical recording medium by an objective lens so that information may be recorded or reproduced.
In an objective lens of the optical pickup apparatus, there is provided an antireflection coating on the surface for improving efficiency of using light. Coating of the antireflection coating is conducted by, for example, a vacuum deposition method or a sputtering method. It has been common to form antireflection coating
11
so that its thickness may vary to be thinner as a position of that thickness is farther from center portion C toward peripheral portion P of objective lens
10
, as shown in FIG.
8
.
Further, thickness of the antireflection coating
11
at the center portion C is established so that reflectance on the center portion C of the objective lens
10
for light entering at an incident angle of 90° may show the minimum value. Namely, the thickness of the antireflection coating
11
is established so that an amount of light passing through the center portion C of the objective lens
10
may be the largest.
Incidentally, it is generally known that the thinner an antireflection coating is in thickness, the more a wavelength-dependence of reflectance for light is shifted to the shorter wave side. Further, in the antireflection coating, it is known that the greater an incident angle of light is, the more a wavelength-dependence of reflectance for light is shifted to the shorter wave side.
In the conventional objective lens
10
, as stated above, antireflection coating
11
is thinner in thickness when a position of that thickness is farther from center portion C toward peripheral portion P of objective lens
10
, and an incident angle of light is greater when a position of the incidence is farther from center portion C toward peripheral portion P.
In the conventional objective lens
10
, therefore, the wavelength-dependence of reflectance for light on the peripheral portion P has been shifted more to the shorter wavelength side than that on the center portion C. Therefore, the wavelength for which the reflectance for light entering at the peripheral portion P shows the minimum value has been shorter than the wavelength for which the reflectance for light entering at the center portion C shows the minimum value.
Accordingly, in the aforementioned conventional objective lens
10
, reflectance of peripheral portion P for a laser beam is higher, although that of central portion C for the laser beam is low, and therefore, an amount of light passing through the peripheral portion P has been less relatively, compared with an amount of light passing through the central portion C. Accordingly, there have been problems such as an increase of a beam spot diameter caused by a decline of converging power for light and a fall of an amount of light of a beam.
To solve these problems, it can be considered that the antireflection coating
11
on the peripheral portion P is made to be thick so that an amount of light passing through the peripheral portion P may be large. However, in this case, thickness of antireflection coating
11
on the center portion C is also increased together with an increase in thickness of the antireflection coating
11
on the peripheral portion P. Therefore, wavelength-dependency of reflectance on the center portion C for light entering at an incident angle of 90° is more shifted to the long wavelength side, and a wavelength becomes longer than that wherein reflectance shows the minimum value, which lowers an amount of light passing through the center portion C.
Namely, in the conventional objective lens
10
, it was impossible to make reflectance on peripheral portion P for light entering obliquely to be small and to make reflectance on center portion C for light entering vertically to be small, at the same time, which has made it difficult to make both light-converging power and an amount of light to be optimum.
In recent years, it has been tried to make a diameter of an optical beam spot small, for a larger capacity of an optical recording medium, and as an example for that, a technology of a higher NA (Numerical Aperture) of an objective lens has been advanced. However, curvature of the lens surface of an objective lens having high NA is great, and therefore, an incident angle for light on the peripheral portion P of the lens is extremely large, and it is a remarkable tendency that thickness of the antireflection coating
11
on the peripheral portion P becomes smaller.
Due to this, an amount of light passing through the peripheral portion P is lowered extremely, and an increase of a spot diameter cannot be controlled despite an objective lens having high NA, resulting in an increase of cross talk and in deterioration of jitter characteristics, which has interfered with a large capacity of an optical recording medium.
SUMMARY OF THE INVENTION
With a background of the problems stated above, an object of the invention is to provide an optical lens wherein a spot diameter can be made small and an amount of light passing the optical lens can be secured, and an optical information recording and reproducing apparatus equipped with the optical lens.
In particular, the object of the invention is to provide an optical lens having an excellent light-converging characteristic and high NA, and to provide an optical information recording and reproducing apparatus wherein a large capacity of an optical recording medium can be realized.
To solve the problems mentioned above, Structure (1) of the invention is an optical lens that is provided on an optical information recording and reproducing apparatus capable of conducting at least one of recording information on an optical recording medium and reproducing of information recorded on an optical recording medium, by converging light on the optical recording medium, wherein an antireflection coating is provided on the lens surface on at least one side thereof, and the thickness of the antireflection coating on the peripheral portion of the lens surface is greater than that of the antireflection coating provided on the center portion of the lens surface.
In the invention described in Structure (1), it is possible to control so that wavelength-dependency of reflectance on the peripheral portion of the lens surface for light may be shifted less to the short wavelength side for wavelength-dependency of reflectance on the center portion of the lens surface, compared with the convention objective lens, because the thickness of the antireflection coating on the peripheral portion of the lens surface is greater than that of the antireflection coating provided on the center portion of the lens surface.
It is therefore possible to control so that reflectance of the peripheral portion of the lens surface for light may not become high even when thickness of the antireflection coating on the center portion is set so that reflectance on the center portion of the lens surface may be low, which is different from the conventional objective lens. It is therefore possible to prevent a fall of an amount of light passing through the peripheral portion of the lens, and to improve a light-converging power to make a spot diameter small and to secure an amount of light passing through the lens, compared with the past.
Structure (2) of t
Epps Georgia
Harrington Alicia M
Konica Corporation
LandOfFree
Optical lens and optical information recording and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical lens and optical information recording and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical lens and optical information recording and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3302669